Basic Math: Examples of decorators

A simple function:



In [30]:

    
def add(a, b):
    """add() adds things"""
    return a + b



In [31]:

    
add(3,4)









    Out[31]:





7

But what if we'd like to log when it's called ?



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def logged_add(a, b):
    print '### %s(%r, %r)' % ('add', a, b)
    result = add(a, b)
    print '### %s(%r, %r) --> %r' % ('add', a, b, result)
    return result



In [33]:

    
logged_add(3,4)









    



### add(3, 4)
### add(3, 4) --> 7






    Out[33]:





7

You could change all calls to this... bleh

( Particularly if you have multple functions you want logged versions of. )

So make a "wrapper function" that will created a logged version of an arbitrary function:



In [34]:

    
def logged(func):
    def wrapper(a, b):
        print '### %s(%r, %r)' % (func.func_name, a, b)
        result = func(a, b)
        print '### %s(%r, %r) --> %r' % (func.func_name, a, b, result)
        return result
    return wrapper

And use it for add:



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add = logged(add)



In [36]:

    
add(3,4)









    



### add(3, 4)
### add(3, 4) --> 7






    Out[36]:





7

And make it more generic (arbitrary number of arguments)



In [37]:

    
def logged(func):
    def wrapper(*args):
        print '### %s(%s)' % (func.func_name, args)
        result = func(*args)
        print '### %s(%s) --> %r' % (func.func_name, args, result)
        return result
    return wrapper



In [38]:

    
def add(a, b):
    """add() adds things"""
    return a + b
add = logged(add)



In [39]:

    
add(3,4)









    



### add((3, 4))
### add((3, 4)) --> 7






    Out[39]:





7

And a couple more:



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def subtract(a, b):
    """subtract() subtracts two things"""
    return a - b
subtract = logged(subtract)

def even(a):
    """even() returns True if the value is even"""
    return a % 2 == 0
even = logged(even)

And use them...



In [41]:

    
add(1, 1)









    



### add((1, 1))
### add((1, 1)) --> 2






    Out[41]:





2



In [42]:

    
add(2, 2)









    



### add((2, 2))
### add((2, 2)) --> 4






    Out[42]:





4



In [43]:

    
subtract(2, 1)









    



### subtract((2, 1))
### subtract((2, 1)) --> 1






    Out[43]:





1



In [44]:

    
even(42)









    



### even((42,))
### even((42,)) --> True






    Out[44]:





True



In [45]:

    
even(43)









    



### even((43,))
### even((43,)) --> False






    Out[45]:





False



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